Metering system for metering fluxes

ABSTRACT

This invention relates to a wire tinning system comprising a molten tinning bath, with a tube having a closed end extending above the bath and an open end immersed in the bath, thereby providing a protective chamber above the level of the bath. Means are provided for drawing a wire to be tinned from the bath and through the protective chamber. There is also provided a reservoir for flux and an adjustable metering valve connected to the discharge of the reservoir. A relatively small diameter tube disposed obliquely with respect to the surface of the melt receives the discharge from the metering valve and delivers it into the protective chamber under conditions that do not disturb the progress of the tinning operation.

United States Patent Trattner et al.

[451 Sept. 16, 1975 METERING SYSTEM FOR METERING FLUXES Inventors: Hermann Trattner; Hans Raab,

both of Munich, Germany Siemens Aktiengesellschaft, Berlin & Munich, Germany Filed: Mar. 8, 1974 Appl. No.: 449,396

Assignee:

Foreign Application Priority Data Mar. 9, 1973 Germany 2311818 Field of Search 118/7, 74, 420, 429, 600;

References Cited UNITED STATES PATENTS 7/1889 Midgley et a1. 117/52 10/1933 Ward 117/52 Marshall 1 17/52 Busch 117/52 Primary Examiner-Mervin Stein Assistant ExaminerSteven Hawkins Attorney, Agent, or Firm--Hill, Gross, Simpson, Van Santen, Steadman, Chiara & Simpson ABSTRACT This invention relates to a wire tinning system comprising a molten tinning bath, with a tube having a closed end extending above the bath and an open end immersed in the bath, thereby providing a protective chamber above the level of the bath. Means are provided for drawing a'wire to be tinned from the bath and through the protective chamber. There is also provided a reservoir for flux and an adjustable metering valve connected to the discharge of the reservoir. A relatively small diameter tube disposed obliquely with respect to the surface of the melt receives the discharge from the metering valve and delivers it into the protective chamber under conditions that do not disturb the progress of the tinning operation.

5 Claims, 2 Drawing Figures METEIRENG SYSTEM FOR METERING FLUXES BACKGROUND OF THE INVENTION ll. Field of the Invention This invention is in the field of wire tinning and provides a system for delivering flux periodically and automatically to a tinning bath.

2. Description of the Prior Art The continuous coating of a wire with a relatively thick soldered film of tin or tin alloy is well known. Normally, the wire is passed vertically or nearly vertically upwards through a solder bath and thereafter through a confining element which regulates the film thickness. In one device for the continuous coating of a copper wire, the wire is guided through a suction nozzle through which it passes with a clearance of about 6.4 millimeters and then the wire passes through a counterflow section in which molten solder flows out of a solder reservoir in a direction opposite to the direction of wire transfer. Ultimately, the wire leaves the solder bath through a shaping die which surrounds the wire with a lateral clearance of at least 0.2 millimeters.

In order to coat metal strips of wires with tin or tin alloy, it is common practice to employ a fluxing agent such as zinc chloride which will dissolve tin oxide at the surface of the bath. The addition of the flux thereby prevents the accumulation of stannic oxide on the bath surface. In devices used for coating steel strips of wires with molten metals or alloys, using exit or pinch rollers in the molten bath, it is well known to surround the point of exit of the wire or strip from the melt with a protective cowl. The cowl extends partially into the melt and is designed to keep the point of exit free of any impurities floating on the bath surface. Zinc chloride is injected into the space formed by the protective cowl in order to prevent oxidation of the bath surface. Thus, the exit rollers employed to coat the wires or strips remain free of impurities.

In an earlier application, a device has been described in which a wire is passed vertically upwards to a tin bath in which the point of exit of the wire is surrounded by a tubular element or a protective chamber partially penetrating into the tin bath. A flux metering device opens into the protective chamber. The flux, normally zinc chloride, in association with the protective chamber serves to reduce the surface tension of the tin bath in the neighborhood of the exit point of the wire. This device operates satisfactorily insofar as it supplies flux to reduce the surface tension of the bath within the pro tective chamber uniformly and in metered quantities. Vapors rising from the tin bath, however, enter the supply line of the metering device so that the supply of flux is not always uniform. This means that the surface ten sion within the protective chamber, that is, in proximity to the wire exit point changes and the tin layer on the wire experiences fluctuations.

SUMMARY OF THE lNVENTION The present invention provides a system which overcomes the aforementioned drawbacks. The present invention provides a metering device which provides a uniform supply of flux to the protective chamber of the tinning system. Through the use of the present invention, the supply of flux to the tinning bath does not disturb the flow characteristics desired in the protective chamber.

The present invention provides a metering device including an adjustable metering valve which communicates with a relatively small diameter tube, the outlet end of which opens into the protective chamber preferably at the wall of the chamber. The tube of relatively small diameter is nevertheless wide in relation to the particles of flux passing through it. The tube is further disposed obliquely in relation to the surface of the melt. With this type of metering device, gases and vapors developing above the molten tin inside the protective chamber can be vented freely through the tube without the stream of flux droplets which are flowing down the tube being hindered in any way. The small diameter tube, thereby acts as a supply means for the flux while much of the cross-sectional area of the tube is available to the stream of gases and vapors flowing in countercurrent direction with respect to the flux.

The tube is inclined in relation to the surface of the tin bath so that the flux simply wets the bottom point of the tube. The mouth of the tube is arranged to be close to the wall of the protective chamber. This insures that the flux metered into the protective chamber runs down the wall thereof and wets the tin bath surface in this zone. In the neighborhood of the cone which forms at the point at which the wire is being drawn through the bath, there is no flow interference from the introduction of the flux. Furthermore, the vapors rising up through the tube heat the flux so that warm flux is supplied to the surface of the molten tin. This counteracts the formation of eddies at the surface of the tin melt of a type which would otherwise arise as a consequence of a steep temperature gradient existing.

The quantity of flux and the interval during which the flux is fed are determined by the metering valve. This metering valve can advantageously be controlled and preset by means of timer elements.

It is also advantageous to add a wetting agent to the flux. By doing so, the uniform supply of the flux to the protective chamber is insured even allowing for the inevitable partial evaporation which takes place.

Both the tube and the wall of the protective chamber may be made of quartz glass .or other transparent material so that the supply of the flux can also be visually monitored. Another transparent glass or quartz tube can be placed centrally of the protective chamber by passing through a plug of synthetic material closing off the upper end of the chamber. This glass tube acts as a secondary heating zone for the tinned wire and also provides an additional source of venting for the protective chamber.

BRIEF DESCRIPTION OF THE DRAWING Other objects, features and advantages of the invention will be readily apparent from the following description of a preferred embodiment thereof, taken in conjunction with the accompanying drawing, although variations and modifications may be effected without departing from the spirit and scope of the novel concepts of the disclosure, and in which:

FIG. 1 is a somewhat schematic view of the metering system of the present invention, with the protective chamber being shown in longitudinal cross-section; and

FIG. 2 is a plan view of the closed protective chamber.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, reference numeral 1 denotes a reservoir for the mixture of flux and wetting agent which will hereinafter be referred to as simply the flux. The flux is fed through a line 2 to a metering valve 3 which is controlled by a solenoid 4. A timer 5 is equipped with a control knob 6 for adjusting the number of metered pulses per unit of time and with a further control knob 7 for adjusting the time of opening of the metering valve 3 for each metering pulse. With the opening of the metering valve 3, a predetermined quantity of flux flows through a very small diameter line 9 into a tube 8. This tube is inclined at an angle W to the horizontal and consists of a transparent material, preferably quartz glass. The internal diameter a may be relatively small but is sufficiently large considering the quantity of flux passing through it so that the flux flows through the tube in the direction of the arrow 12 toward a protective chamber 13 solely along the bottom surface 11 of the tube.

The wall of the protective chamber consists of a tubular portion 14 of quartz glass having an open-ended bottom 14 which penetrates into the molten tin 22. As best seen in FIG. 2, the tube 8 passes laterally through a plug 16 closing off the protective chamber 13. The plug 16 is formed of a heat resistant synthetic material.

Passing centrally through the plug 16 there is a vent pipe 17 also composed of quartz glass through which a tinned wire 18 passes upward in the direction of the arrow 19. This vent pipe 17 constitutes a secondary heating zone for the tinned wire. On drawing the wire through the molten tin inside the protective chamber, an exit cone 20 forms and this cone must not undergo any fluctuation during the drawing phase. Consequently, the flux, preferably zinc chloride, flows through the tube 8 and enters the protective chamber near the wall 21. In so doing, it wets the wall 21 of the tubular member 14 and then drops on the molten tin surface 22. Disturbances in the surface of the bath of the kind which could arise with the dripping of the flux or due to a chemical reaction are thus very largely avoided. The gases or vapors which develop inside the protective chamber 13 flow essentially in the direction of the arrows 23 through the vent pipe 17. Part of the gases or vapors, however, also flow in the direction of the arrow 24 through the tube 8 but the tube is of sufficient diameter to accommodate such gaseous flow without interfering with the supply of flux to the protective chamber.

It should be evident that various modifications can be made to the described embodiments without departing from the scope of the present invention.

We claim as our invention:

1. A wire tinning system comprising a molten tinning bath, a tube having an open end immersed in said bath and providing a protective chamber above the level of said bath, means for drawing a wire from said bath and through said protective chamber, a reservoir containing flux and having a discharge portion, an adjustable metering valve connected to said discharge portion of said reservoir, and a flux delivery tube disposed obliquely with respect to the surface of said molten tin ning bath, the flux delivery tube receiving flux from said metering valve and delivering it into said protective chamber.

2. The system of claim 1 in which said flux delivery tube is composed of a transparent material.

3. The system of claim 1 in which the mouth of the flux delivery tube discharges flux in close proximity to a wall of the protective chamber.

4. The system of claim 1 in which said metering valve communicates with said flux delivery tube through a tube of smaller diameter.

5. The system of claim 1 which includes a first adjustable timer controlling the rate at which said metering valve opens, and a second adjustable timer controlling the duration of the intervals during which said metering 

1. A wire tinning system comprising a molten tinning bath, a tube having an open end immersed in said bath and providing a protective chamber above the level of said bath, means for drawing a wire from said bath and through said protective chamber, a reservoir containing flux and having a discharge portion, an adjustable metering valve connected to said discharge portion of said reservoir, and a flux delivery tube disposed obliquely with respect to the surface of said molten tinning bath, the flux delivery tube receiving flux from said metering valve and delivering it into said protective chamber.
 2. The system of claim 1 in which said flux delivery tube is composed of a transparent material.
 3. The system of claim 1 in which the mouth of the flux delivery tube discharges flux in close proximity to a wall of the protective chamber.
 4. The system of claim 1 in which said metering valve communicates with said flux delivery tube through a tube of smaller diameter.
 5. The system of claim 1 which includes a first adjustable timer controlling the rate at which said metering valve opens, and a second adjustable timer controlling the duration of the intervals during which said metering valve opens. 